Vertically moored platforms

ABSTRACT

This invention relates to a structure floating on a body of water. Three or more spar buoy-type floats support the structure above the water. The structure is connected to anchors in the floor of the body of water by elongated members such as large diameter pipe. There are no other anchoring connections in the system. Each spar buoy has a unique structure so that vertical forces and overturning moments on the floating structure are minimized. The spar buoys have a buoyancy means having a volume of two parts. The first part can be defined as resulting from a straight, vertical, prismatic shape which runs the entire vertical length of the buoyancy means. The volume of this prismatic portion comprises between about 40 and 80 percent of the total displacement. The buoyancy means have a second or auxiliary volume of displacement which runs considerably less than the vertical length of the prismatic portion. This critical arrangement of buoyancy between these two parts as taught in this invention minimizes mooring forces imposed on the vertical elongated members, such as occur to react forces on the structure due to passing waves.

Blenkarn VERTICALLY MOORED PLATFORMS [72] Inventor. Kenneth A. Blcnkarn, Tulsa, Okla.

[73] Assignee: Amoco Production Company, Tulsa, Okla.

[22] Filed: Mar. 9, 1970 21] Appl. No.: 17,485

Related US. Application Data [63] Continuation-impart of Ser. No. 754,628, Aug. 28,

1968, abandoned.

[52] US. Cl. ..ll4/0.5 D, 61/465 [51] int. Cl. .3631: 35/00, B63b 35/44 [58] Field of Search ..l14/0.5, 0.5 D, 43.5; 61/465 [56] References Cited UNITED STATES PATENTS 2,399,656 5/1946 Armstrong ..1l4/0.5 D 3,224,401 12/1965 Kobus ...l14/0.5 D 2,939,291 6/1960 Schurman et al.. 114/05 D 3,154,039 10/1964 Knapp .114/O.5 D 3,327,780 6/1967 14/0.5 D X Primary Examiner-Trygve M. Blix Attorney-Paul F. Hawley and John D. Gassett [57] ABSTRACT This invention relates to a structure floating on a body of water. Three or more spar buoy-type floats support the structure above the water. The structure is connected to anchors in the floor of the body of water by elongated members such as large diameter pipe. There are no other anchoring connections in the system. Each spar buoy has a unique structure so that vertical forces and overturning moments on the floating structure are minimized. The spar buoys have a buoyancy means having a volume of two parts. The first part can be defined as resulting from a straight, vertical, prismatic shape which runs the entire vertical length of the buoyancy means. The volume of this prismatic portion comprises between about 40 and 80 percent of the total displacement. The buoyancy means have a second or auxiliary volume of displacement which runs considerably less than the vertical length of the prismatic portion. This critical arrangement of buoyancy between these two parts as taught in this invention minimizes mooring forces imposed on the vertical elongated members, such as occur to react forces on the structure due to passing waves.

42 Claims, 40 Drawing [Figures 8 3 6 RM m 3 22 sheets sheat 2 INVENTOR. KENNETH A. BLENKARN ATTORNEY Patented March 14, 1972 3,648,638

22 Sheets-Sheet 5 INVENTOR. KENNETH A. BLENKARN BY M A T TORNEY Patented March 14, 1972 3,648,638

22 Sheets-Sheet 4.

O I I 1- 1 FIG. 4

INVENTOR. KENNETH A. BLENKARN ATTORNEY Patented March 14,, 1972 22 Sheets-Sheet 5 l0 TOTAL DISPLACEMENT 92 STILL WATER DRAFT= I25 FT KENNETH A. .BLENKARN INVENTOR.

WTQM ATTORNEY VARIATION OF NET VERTICAL FORCE DISRL...)

Patented March 14, 197 3,648,638

22 Sheets-Sheet 6 T 5L2 FT, I I0 SEC. WAVE 0 l FIG. 6A

. I00 FT, l4 SEC. WAVE -.30 I00 FT, 20 SEC. WAVE I00 FT, 20 SEC. wAvE WAVE 0 FIG. 68

SEC. WAVE -.|o

.2 FT, IO SEC. WAVE I00 FT, l4 SEC.WAVE I FIG. 60

I00 FT, 20 SEC.WAVE

TROUGH LEADING CREST CREST FOLLOWING CREST INVENTOR.

BY am ATTORNEY Patented March 14, 1972 3,648,638

22 Sheets-Sheet 7 SlNGLE AMPL.

1 OF PITCH KENNETH A. BLENKARN f, .INVENTOR.

3 BY FIG. IO %4 fiM ATTORNEY Patented March 14, 1972 OVERTURNING MOMENT m FT. KIPS 22 Sheets-Sheet 8 OVERTURNING MOMENTS I0O FT. -20 SEC. WAVE 200 NET OVERTURNING MOMENT IOO- WIND vERTIcAL WIND DRAG LIFT HORIZONTAL DRAG \MOMENT DUE TO COUPLING 0F HORIZONTAL FORCES RIsER ENO MOM -I00- -I5O- -200 I \M FOLLOWING TROUGH LEADING CREST FOLLOwINO CREST CREST CREST FIG. 8

KENNETH A. BLENKARN INVENTOR.

ATTORNEY.

Patented March 14, 1972 3,648,638

22 Sheets-Sheet 9 6% i 4 0- 2 a s E m a as i. w 3 Z O P- Lu 0 g 0 f, 5|.2'IOSEC. LL 3 WAVE 0 Lu 6 .O5- l g g 4 |00'-|4 SEC. WAVE 2 C1: -.|0-.

|o0-20 SEC. WAVE -.I5- I FOLLOWING TROUGH LEADING CREST FOLLOWING CREST CREST CREST FIG. 9

BY%Z% a A T TORNE Y.

Patented March 14,, 1972 NET VARIATION OF MOORING FORCE, LEG NO 0 DISPL. PER LEG) 22 Sheets-Sheet 1O NET VERTICAL FORCE IOO ET,

I00 FT, IA

FIG. HA 0 VARIATION DUE TO COUPLING OF NET -O.l35 VERTICAL FORGE ON VARIATION DUE TO INDIVIDUAL. LEGS VARIATION DUE TO OVERTURING IOOFT, ZOSEGWAVE MOMENTS -0.I35 -O.I37

FOLLOWING TROUGH LEADING CREST CREST SLZ FT Io SEC. WAVE CREST FOLLOWING CREST PLATFORM POSITION RELATIVE TO WAVE KENNETH A. BLENKARN INVENTOR.

BY ATTORNEY Patented March 14, 1972 NET VARIATION OF MOORING FORCE, LEG IIIOQ o DISPL PER LEGI 22 Sheets-Sheet l1 VARIATION DUE TO 50 NET VERTI1CAL FORCE\ VARIATION DUE TO OVERTURING MOIIIIEN I00 FT, 20 SEC WAVE (VARIATION COUPLING VERTICAL VARIATION LEG NO. 4

FIG. I2A

DUE TO OF NET FORGE ON INDIVIDUA L LEGS FIG I25 5I2 FT,

IO SEC. WAVE 2Q IOO FT, I4 SEC. WAVE I IOO PT, 20 SEC. WAVlE FOLLOWING TROUGH LEADING CREST FOLLOWING CREST CREST CREST PLATFORII/I POSITION RELATIVE TO WAVE KENNETH A. BLENKARN INVENTOR.

ATTORNEY Patented 7 March 14, IlIIji.

(' 3 DISPL PER LEG) 22 Sheets-Sheet 1 .2

VARIATION CREST LEG N04 /VARIATION DUE To NET I/ERTIOAI. FOROE FIG. BA (VARIATION 1: T DUE TO COUPLING OF gg g l' VARIATION DUE TO 'NDMDUAL LEGS OIVERTURNINGMOMENTS IOO FT, 20 SEC wAvE I0 SEC. WAVE FIG. I3 B T /IOO FT, 2osEOwAvE IOO FT, I4sEc.wAvE FOLLOWING TROUGH LEADING CREST FOLLOWING CREST CREST PLATFORM POSITION RELATIVE TO WAVE KENNETH A. BLENKARN INVENTOR.

ATTORNEY 7 PM@@&@& Man-ah 3,548,638 22 shets-Sheet 1s MAXIMUM DESIGN WAVE HEIGHT=|OO FT. LEG SPACHNG 56G FT. ERAFT I25 FT. TQTAL DISPLACEMENT 28,675 kips PLATFORM MASS l8,675 kips TOTAL MOORlNG FORCE |0,000 kips 0.5 |.O |.5 r 2.0 2.5 3.0 FIG. [4

KENNETH A. BLENKARN INVENTOR.

all (7: fl w ATTORNE Y pammmfi 14, 1972 22 Sheets-Sheet l4 MAxlMuM OEsTON \NAvE HE|GHT=IOO FT.

LEG SPACING=I6O FT.

L ORAFT=125 FT.

TOTAL O1sPLAOEMENT=28,eT5 kips PLATFORM MASS=I8,675 kips TOTAL MOORING FORCE=l0,000kips 05 L0 L5 v 2'.O 5 0 F|G.l5B

L ELL 0.5 2 H 02 .20 18161414161820 IATIMAX) m BEsT COMBINATION OF PARAMETERS b RANGE OF MOsT PRACTICAL COMBINATIONSO162 I l l 0.5 L0 1.5 2.0 2.5 3.0

FIG. 15A

ATTORNEY.

Pmwm TTT K,

22 Sheets-Sheet 15 A T TORNEY.

3 XIMUM DESIGN WAVE HEIGHT=IOO FT.

LEG sPAcTTTe I40 FT. 0 2 DRAFT=|25 FT.

TOTAL, D|SPLACEMEMT=28,675 kips OT -PLATFORM MASS T8575 kips 0 TOTAL TyTooRTTTe ToRcE=Tppoo kip s I To If) V 2.0 2.5 3.0

FIG. I68

0.3 I IMAX O I I l l J 0.5 L0 L5 r 2.0 2.5 3.0

' FIG IGA KENNETH A. BLENKARN INVENTOR.

Patented March 14,, 197

22 Shams-Sheet 16 MAXIMUM DESIGN WAVE HEIGHT=|OO FT.

15c SPACING=2OO FT. 0RAFT=|25 FT TOTAL DISPLACEMENT=28,675 kips O PLATFORM MASS= |8,675 kips TOTAL MOORING FORCE=I0,000 kips l I I l 0.5 |.0 l5 2.0 2.5 3.0

O l l l l 0.5 L0 L5 V 2.0 2.5 3.0 FIG [7A KENNETH A. BLENKARIV INVENTOR.

ATTORNEY.

Patented March 14, 1972 22 Sheets-Sheet l7 FIG. |8B

MAXIMUM DESIGN WAVE HEIGHT=IOO FT. LEG SPACING=I6O FT. DRAFT=|OO FT.

TOTAL DISPLACEMENT=28,675 kips PLATFORM MASS |8,675 kips TOTAL MOORING FORCE=I0,000kips l l l l 0.5 L0 L5 r 2.0 2.5 3.0

0 I l I l l KENT/v5 TH A. BLENKAR/V INVENTOR.

A T TOR/V5 Y.

Patented March 14, 1972 MAXIMUM DESIGN WAVE HEiGHT I00 FT.

22 Sheets-Sheet l8 0 LEG SPACING=I6O FT.

'O 2 DRAFT= I50 FT.

TOTAL DISPLACEMENT 28,675 kips O l-PLATFORM MASS= |8,675 kips TOTAL MOORING FORCE=IO,OOO kips I 0.5 1.0 l5 r 2.0 2.5 3.0

FIG. |9B

L/ i( m s 0.6- H 2 H O.3- IATI MAX l l I 0.5 1.0 |.5 V 2.0 2.5 3.0

. M KENNETH A. BLENKARN INVENTOR.

A T TORNE Y.

Patented March 14, 1972 3,648,638

22 Sheets-Sheet 19 RAT|= (Wm /H =00 150 SPACING= T60 FT. 0 2 DRAFT =75 FT.

' TOTAL DISPLACEMENT=28,675 kips PLATFORM MASS |0,0T5 kips TOTAL MOORING FORCE=I0,000 kips l I l l l 0.5 |.0 T5 y 2.0 2.5 30

FIG. 20B

MAX 0.5-

2( H 0.4- \g 03 I IMAX 20).|6f.20=( b .l8 .l8

O l l l 0 KENNETH A. BLENKARN INVENTOR.

A T TORNE X 

1. A floating structure having limited lateral movement for use in a body of water which comprises: a working deck; buoyancy means for supporting said working deck, said buoyancy means including a plurality of slender vertical float members; anchor means in the floor of the body of water; horizontally spaced-apart, parallel, elongated members interconnecting the said buoyancy means and said anchor means whereby said deck is maintained parallel to and at a substantially constant angle with reference to the horizontal; each said vertical float member of said buoyancy means having prismatic volume resulting from a straight, vertical, prismatic shape which runs the entire vertical length of the buoyancy means, the volume of the prismatic portion comprising between about 40 and 80 percent of the total displacement of the buoyancy means, and the structure having an auxiliary buoyancy portion having a volume of displacement between about 20 and about 60 percent of the total displacement of the buoyancy means, said auxiliary volume Being placed below the trough of an expected maximum wave; said platform and buoyancy means being free of any anchoring connection with the water bottom other than said parallel elongated members.
 2. A structure as defined in claim 1 in which the volume of the prismatic portion comprises between about 40 and about 60 percent of the total displacement of the buoyancy means.
 3. A structure as defined in claim 1 in which the ratio hmax/H is about 0.8 in which hmax is the height of an expected maximum wave and H is the still water draft.
 4. A structure as defined as claim 3 in which the still water draft is between about 75 feet and about 150 feet.
 5. A structure as defined in claim 1 in which the structure is so designed as to have a still water draft between about 75 feet and about 150 feet.
 6. An apparatus as defined in claim 1 including pivotal means connecting the lower ends of said elongated members with said anchor means and additional pivotal means connecting the upper ends of said elongated members with said buoyancy means.
 7. An apparatus as defined in claim 1 including horizontal fins attached to the lower portion of said buoyancy means.
 8. An apparatus as defined in claim 7 including means to move said horizontal fins about a horizontal axis.
 9. An apparatus as defined in claim 1 in which said elongated members are tubular members.
 10. An apparatus as defined in claim 1 including cross bracing between the vertical float means, said cross bracing being restricted to the areas below the still water line.
 11. A floating structure for use in the body of water having an expected maximum wave which comprises: a deck; buoyancy means rigidly supporting said deck, said buoyancy means including at least three slender, vertical float members, each such float member having two parts, the first part resulting from a straight, vertical, prismatic shape which runs the entire vertical length of the vertical float member, the volume of the prismatic portion comprising between about 40 and about 80 percent of the total displacement of the vertical float member, and an auxiliary portion exterior said prismatic portion and, comprising between about 20 and about 60 percent of the total displacement of the buoyancy means below still water, said auxiliary portion being placed below the trough of the expected maximum wave; anchor means at the bottom of said body of water; an elongated member connecting each said vertical float member and said anchor means, said elongated members being parallel; said structure being free of any anchoring connection with the water bottom other than said parallel elongated members.
 12. A structure as defined in claim 11 in which the volume of the prismatic portion of the vertical float member is between about 45 and 65 percent of the total displacement of the vertical float member and the auxiliary portion exterior of said prismatic portion comprises between about 55 and about 35 percent of the total displacement of the buoyancy means below still water.
 13. An apparatus as defined in claim 11 including pivotal means connecting the lower ends of said elongated members with said anchor means and additional pivotal means connecting the upper ends of said elongated members with said buoyancy means.
 14. An apparatus as defined in claim 11 in which said elongated members are tubular members.
 15. A structure as defined in claim 11 in which the ratio hmax/H is about 0.8 in which hmax is the expected maximum wave height and H is the still water draft.
 16. A structure as defined in claim 11 with a ratio hmax/H that is between about 0.65 and about 1.00 where hmax is the expected maximum wave height and H is the still water draft.
 17. A floating structure for use in a body of water having aN expected maximum wave height hmax which comprises: a deck; buoyancy means rigidly supporting said deck, said buoyancy means providing a total still water displacement B and including at least one slender vertical float member having a still water draft H, comprising two parts, the first part resulting from a straight prismatic shape which runs the entire vertical length of the vertical float member and an auxiliary portion exterior to said prismatic portion having an overall vertical length L, said auxiliary portion being placed below the trough of the expected maximum wave, for which the shape of the slender, vertical float member is defined by a value of r, said parameter r being the ratio of the maximum radius of the auxiliary portion to the radius of the prismatic portion, which value r is between about (r3 - (0.3441 kips/ft.2)(H2/B)) and about (r4 + (34.41 kips/ft.)(H/B)) where r3 is determined from Equations (29) through (31) and r4 is determined from Equations (32) through (34); anchor means at the bottom of said body of water; elongated member interconnecting each said slender vertical float member and said anchor means, if there is more than one vertical float member, the said elongated members associated therewith are parallel; said structure being free of any anchoring connection with the water bottom other than said elongated member.
 18. A structure as defined in claim 17 in which the ratio (hmax/H) is about 0.8.
 19. A structure as defined in claim 17 in which the ratio hmax/H is between about 0.65 and about 1.00.
 20. A structure as defined in claim 17 in which said elongated members are tubular members.
 21. A structure as defined in claim 17 in which there are at least three slender vertical float members and an elongated member connecting each said slender vertical float member and said anchor means, said elongated members being parallel; said structure being free of any anchoring connecting with the water bottom other than said elongated members.
 22. A structure as defined in claim 21 in which the ratio hmax/H is between about 0.65 and about 1.00.
 23. A structure as defined in claim 22 in which the ratio hmax/H is about 0.8.
 24. A structure as defined in claim 17 in which r is between about r3 and r4.
 25. A floating structure for use in a body of water and having an expected maximum wave height hmax which comprises: a deck; buoyancy means rigidly supporting said deck, said buoyancy means providing a total still water displacement B and including at least one slender vertical float member, said vertical float member having a still water draft H, comprising two parts, the first part resulting from a straight prismatic shape which runs the entire vertical length of the vertical float member and an auxiliary portion exterior to said prismatic portion having an overall vertical length L, said auxiliary portion being placed below the trough of the expected maximum wave, for which the shape of the slender, vertical float member is defined by a value of r, said parameter r being the ratio of the maximum radius of the auxiliary portion to the radius of the prismatic portion, which value r is between about (r1 - (0.3441 kips/ft.2)(H2/B)) and about (r2 + (34.41 kips/ft.)(H/B)) where r1 is determined from Equations (20) through (22) and r2 is determined from Equations (23) through (25); anchor means at the bottom of said body of water; an elongated member interconnecting each said vertical float membEr and said anchor means, if there is more than one vertical float member, the said elongated members associated therewith are parallel; said structure being free of any anchoring connection with the water bottom other than said parallel elongated members.
 26. An apparatus as defined in claim 25 including pivotal means connecting the lower ends of said elongated members with said anchor means and additional pivotal means connecting the upper ends of said elongated members with said buoyancy means.
 27. An apparatus as defined in claim 25 in which said elongated members are tubular members.
 28. A structure as defined in claim 25 in which there are at least three slender vertical float members and an elongated member connecting each said slender vertical float members and said anchor means, the said elongated members associated therewith being parallel; said structure being free of any anchoring connected to the water bottom other than said elongated members.
 29. A structure as defined in claim 28 in which the ratio hmax/H is between about 0.65 and about 1.00.
 30. A structure as defined in claim 29 in which the ratio hmax/H is about 0.8.
 31. A structure as defined in claim 25 in which the value of r is between about r1 and r2.
 32. A floating structure as defined in claim 25 in which the ratio hmax/H is between about 0.75 and about 0.85.
 33. A structure as defined in claim 32 in which the ratio hmax/H is about 0.8.
 34. A floating structure for use in a body of water having an expected maximum wave height hmax which comprises: a deck; buoyancy means rigidly supporting said deck, said buoyancy means providing a total still water displacement B and including at least one slender vertical float member having a still water draft H, each said vertical float member comprising two parts, the first part resulting from a straight prismatic shape which runs the entire vertical length of the vertical float member and an auxiliary portion exterior to said prismatic portion having an overall vertical length L, said auxiliary portion being placed below the trough of the expected maximum design wave, for which the shape of the slender, vertical float member is defined by a value of r, said parameter r being the ratio of the maximum radius of the auxiliary portion to the radius of the prismatic portion, which value r is between about (rbt -(0.3441 kips/ft.2)(H2/B)) and about (rbt + (34.41 kips/ft.)(H/B)) where rbt is determined from Equations (10), (16) and (17); anchor means at the bottom of said body of water; an elongated member connecting each said vertical float member and said anchor means, said elongated members associated therewith being parallel; said structure being free of any anchoring connection with the water bottom other that said parallel elongated members.
 35. An apparatus as defined in claim 34 including pivotal means connecting the lower ends of said elongated members with said anchor means and additional pivotal means connecting the upper ends of said elongated members with said buoyancy means.
 36. A structure as defined in claim 34 in which there are at least three slender vertical float members and an elongated member connecting each said slender vertical float members and said anchor means, the said elongated members associated therewith being parallel; said structure being free of any anchoring connection to the water bottom other than said elongated members.
 37. An apparatus as defined in claim 34 in which said elongated members are tubular members.
 38. A structure as defined in claim 34 in which the value of r is equal to rbt.
 39. A structure as defined in claim 34 wherein said ratiO hmax/H is about 0.8.
 40. A structure as defined in claim 36 in which the ratio hmax/H is about 0.8.
 41. A floating structure for use in a body of water which comprises: a deck; buoyancy means rigidly supporting said deck, said buoyancy means providing a total still water displacement between about 15, 000,000 pounds and about 60,000,000 pounds and including at least three slender, vertical float members, each such vertical float member having a still water draft between about 75 feet and about 150 feet and comprising two parts, the first part resulting from a straight, vertical prismatic shape which runs the entire vertical length of the vertical float member and an auxiliary portion exterior to said prismatic portion, said auxiliary portion being placed below the trough of the maximum design wave, for which the shape of the slender, vertical float member is defined by either (a) values of p and r which when plotted as a point falls into the shaded regions of either FIGS. 15B through 23B or falls into shaded regions obtained by a linear interpolation between the shaded regions of these figures, said interpolation being made on the basis of still water displacement and still water draft, or (b) values of (L/H) and r which when plotted as a point falls into the shaded regions of either FIGURES 15A through 23A, or falls into shaded regions obtained by a linear interpolation between the shaded regions of these figures, said interpolation being made on the basis of still water displacement and still water draft; anchor means at the bottom of said body of water; an elongated member interconnecting each said buoyancy means and said anchor means, said elongated members associated therewith being parallel; said structure being free of any anchoring connection with the water bottom other than said parallel elongated members.
 42. An apparatus as defined in claim 41 in which said elongated members are tubular members. 